1. Field of the Invention
This invention relates generally to tabletted detergents. More particularly, the invention relates to a process for the production of detergent tablets, in which advantageous product properties, such as hardness, fracture resistance and good solubility, are combined with process advantages, such as minimal outlay on machinery, low tabletting forces and low temperatures.
Detergent tablets have been widely described in the prior-art literature and are becoming increasingly popular among consumers because they are easy to dose. Tabletted detergents have a number of advantages over powder-form detergents: they are easier to dose and handle and, by virtue of their compact structure, have advantages in regard to storage and transportation. Accordingly, detergent tablets are also comprehensively described in the patent literature.
2. Discussion of Related Art
Thus, EP-A-0 522 766 (Unilever) describes tablets of a compacted particulate detergent composition, the particles being at least partly coated with a material which acts both as a binder and as a disintegrating agent when the tablets are dissolved in water. The document in question also refers to the general difficulties involved in producing tablets combining adequate stability with good dissolvability. The particle size in the mixture to be tabletted should be above 200 .mu.m and the upper and lower limits to the individual particle sizes should not be more than 700 .mu.m apart from one another.
Other documents concerned with the production of detergent tablets include EP-A-0 716 144 (Unilever), which describes tablets with an outer shell of water-soluble material, and EP-A-0 711 827 (Unilever) which mentions a citrate having defined solubility as an ingredient.
The use of binders, more particularly polyethylene glycol, is disclosed in EP-A-0 711 828 (Unilever) which describes detergent tablets produced by tabletting a particulate detergent composition at temperatures between 28.degree. C. and the melting point of the binder, tabletting always being carried out below the melting temperature. It is apparent from the Examples of this document that the tablets produced in accordance with its teaching have higher fracture resistances when tabletting is carried out at elevated temperature.
All the documents cited above use high tabletting pressures above 15 N/cm.sup.2 in the tabletting process to obtain sufficiently stable tablets. The tabletting processes are optionally carried out at elevated temperature because stability is said to be further increased by a form of "sintering".
The problem addressed by the present invention was to provide a simplified process for the production of tablets which would out-perform known tablets in regard to fracture resistance, stability in storage and dissolving behavior.